Quantum mechanical calculations on cellulose-water interactions: structures, energetics, vibrational frequencies and NMR chemical shifts for surfaces of Iα and Iβ cellulose

Periodic and molecular cluster density functional theory calculations were performed on the I alpha (001), I alpha (021), I beta (100), and I beta (110) surfaces of cellulose with and without explicit H2O molecules of hydration. The energy-minimized H-bonding structures, water adsorption energies, vibrational spectra, and C-13 NMR chemical shifts are discussed. The H-bonded structures and water adsorption energies (Delta E-ads) are used to distinguish hydrophobic and hydrophilic cellulose-water interactions. O-H stretching vibrational modes are assigned for hydrated and dry cellulose surfaces. Calculations of the C-13 NMR chemical shifts for the C4 and C6 surface atoms demonstrate that these delta(13)C4 and delta(13)C6 values can be upfield shifted from the bulk values as observed without rotation of the hydroxymethyl groups from the bulk tg conformation to the gt conformation as previously assumed.